The present invention relates to an optical displacement sensor for measuring a displacement such as a length of a measurement object according to a light section method, triangulation or the like, and in particular to an optical displacement sensor which allows the state of the surface of the measurement object to be observed on the screen of a video monitor.
Two examples of sensor units for such optical displacement sensors are shown in FIG. 43 (regular reflection surface type) and FIG. 44 (irregular reflection surface type).
Referring to FIG. 43, a denotes a sensor head unit, b denotes measurement light (a red laser beam having a circular cross section or a linear cross section, for instance) which is emitted from the sensor head unit mounted at a prescribed position and impinged obliquely downward onto a measurement object, c denotes measurement light which is reflected by the surface of the measurement object and advances obliquely upward onto the sensor head unit, d denotes the measurement object of a regular reflection surface type such as a glass plate or a metallic plate having a smooth surface, and e denotes diffused reflected light produced by the reflection of the measurement light by the surface of the measurement object. The light axis of the measurement light exiting from the unit a and the light axis of the incident measurement light c directed to the unit a are arranged symmetric to each other at a same inclination angle.
Referring to FIG. 44, a denotes a sensor head unit, d denotes a measurement object of a irregular reflection surface type, f denotes measurement light (a red laser beam having a circular cross section or a linear cross section, for instance) which is emitted from the sensor head unit vertically downward onto the measurement object, g denotes measurement light which is reflected by the surface of the measurement object and advances obliquely upward onto the sensor head unit, and h denotes diffused reflected light produced by the reflection of the measurement light by the surface of the measurement object.
The reflected measurement light c and g received by the sensor head unit forms an image on the light receiving surface of the imaging device (such as a one dimensional CCD and a two dimensional CCD) via a light receiving optical system (such as a lens assembly), and is converted into a video signal including the radiated light image (a bright spot or line) of the measurement light by using the photoelectric conversion capability of the imaging device. The video signal thus obtained is forwarded to a controller unit now shown in the drawing, and is used for a computation for displacement measurement based on triangulation.
To accurately measure a displacement (such as a displacement in the vertical direction) of a desired position on the measurement object, it is necessary to coincide the radiated position of the measurement light b and f with the measurement position in a highly accurate manner. When the measurement light consists of visible laser light (such as red laser light), the registration between the measurement position and the radiated position of measurement light can be accomplished by moving the radiated light image of the measurement light to the desired measurement position while visually observing the radiated light image.
However, such conventional displacement sensors are known to have a number of problems.
(1) When the measurement has surface irregularities, the work of adjusting the radiated position of the measurement light right onto the measurement point, and the work of verifying that the measurement light is accurately radiating upon the measurement point involve some difficulty when performed with a direction observation using the naked eye.
(2) In FIGS. 43 and 44, if the measurement distance L which is a displacement measurement range is short, and the sensor head unit a and the measurement object are close to each other, because the sensor head unit a closely covers the measurement position from above, the field of view of the operator is obstructed by the sensor head unit a, and the operator experiences a difficulty in viewing the radiated light image of the measurement light, and is unable to properly carry out the work of achieving a registration between the measurement position and the radiated position of measurement light.
(3) Displacement sensors using a conventional two dimensional imaging device include those allowing the illuminated light image of the measurement light captured by the two dimensional imaging device to be displayed on an image monitor. However, the illuminated light image of the measurement light shows itself far brighter than the surrounding surface of the measurement object. This is because the intensity of the measurement light, the lighting timing of the measurement light and the shutter timing of the two dimensional imaging device are determined in such a manner that the illuminated light image of the measurement light is appropriately imaged but the surrounding surface of the measurement object appears substantially darker in comparison because the image of the shape and pattern of the surface of the measurement object surrounding the measurement point should not interfere with the measurement. Therefore, even though the image monitor allows the radiated light image of the measurement light to be observed, but because the surrounding surface of the measurement object is not shown on the screen, it is not possible to verify the positional relationship between the radiated light image and the surface of the measurement object on the image monitor.
The present invention was made in view of such problems, and its primary object is to provide a displacement sensor which allows the positional relationship between the radiated light image and the surface of the measurement object to be verified on the image monitor, and component technology to such a displacement sensor.
These and other objects, and advantages of the present invention will become apparent to a person skilled in the art in view of the following description.
The sensor head of the present invention may have a sensor head and a controller either integrally or separately. The term xe2x80x9cintegralxe2x80x9d as used herein means that the sensor head unit and the controller unit are accommodated in a common housing. The term xe2x80x9cseparatelyxe2x80x9d as used herein means that the sensor head unit and the controller unit are accommodated in separate housings. As for the image monitor, it may be provided with a separate housing or may also be accommodated in the housing of the controller unit, for instance.
The sensor head may comprise a measurement light emitting optical system for emitting measurement light onto a measurement position of an measurement object from a prescribed angle, an image acquiring optical system for capturing an image by viewing the measurement position of the measurement object and a surrounding region from an angle different from that of the measurement light emitting optical system, and a two dimensional imaging device for photoelectrically converting an image obtained by the image acquiring optical system into a video signal corresponding to the image.
The xe2x80x9cmeasurement light emitting optical systemxe2x80x9d as used herein may comprise a lens array defining a light emitting light path, and may also comprise other optical elements such as mirrors and filters. A light source for emitting light may be incorporated in the system or may be drawn from an external source via an optical fiber. An example of a light emitting light source consists of a red laser diode. The xe2x80x9cemitting anglexe2x80x9d may be either a regular reflective surface type described in connection with FIG. 43 or an irregular reflective surface type described in connection with FIG. 44.
The controller may be adapted to control an imaging condition associated with a brightness of the image in the form of the video signal, and to operate under a measurement mode and an observation mode.
When the controller operates under the measurement mode, with a light source for measurement turned on, the imaging condition being adjusted in such a manner that a measurement light radiated light image can be imaged at an appropriate brightness but a surrounding part of the measurement object is substantially darker than the appropriate brightness, and a desired displacement being computed according to the video signal obtained by the two dimensional imaging device. When the controller operates under the observation mode, the imaging condition being adjusted in such a manner that the measurement position and the surrounding part of the measurement object can be imaged both at an appropriate brightness, and an image of the measurement position of the surface of the measurement object and the surrounding region being displayed on the screen of an image monitor according the video signal obtained by the two dimensional imaging device.
According to this structure, the positional relationship between the measurement light radiated light image and the measurement objection can be verified on the image monitor. Therefore, even when the sensor head closely overlies the intended measurement position or the intended measurement position has an irregular surface that prevents the shape of the intended measurement position from being directly identified with the naked eye and causes difficulty in identifying where the measurement light is radiated, it is possible to obtain the intended measurement result in a reliable manner through accurate positioning of the radiated light image onto the measurement position.
The xe2x80x9cimaging condition which is adjusted under the measurement modexe2x80x9d includes the brightness control for the measurement light source and/or exposure time for the two dimensional imaging device. When the measurement light source is lighted in pulses, the brightness of the measurement light source may mean the average brightness which is proportional to the produce of an instantaneous brightness and the duration time.
The controller under the observation mode may be adapted to adjust the imaging condition in such a manner that the measurement light radiated light image is not imaged at all or substantially darker than the appropriate brightness. In this case, the xe2x80x9cimaging condition which is adjusted under the observation modexe2x80x9d may include a turned on or turned off state of the measurement light source, the brightness control for the measurement light source and/or the exposure time for the two dimensional imaging device.
The imaging condition that would cause the measurement light radiated light image to be not imaged at all or imaged substantially darker than an appropriate brightness may include turning off the measurement light source, reducing the brightness of the measurement light source, turning on the measurement light source in pulses and assigning the period between the turned on states of the measurement light source to the exposure period of the two dimensional imaging device.
The controller under the observation mode may be adapted to adjust the imaging condition in such a manner that the measurement light source is turned on, and the measurement light radiated light image and the surrounding region are both imaged at an appropriate brightness. The xe2x80x9cimaging condition which is adjusted under the observation modexe2x80x9d at this time may include the brightness control for the measurement light source and/or the exposure time for the two dimensional imaging device.
The observation mode may include a first observation mode and a second observation mode, the controller under the first observation mode adjusting the imaging condition in such a manner that a measurement light radiated light image is not imaged at all or imaged substantially darker than an appropriate brightness, the controller under the second observation mode adjusting the imaging condition in such a manner that with the measurement light source turned on the measurement light radiated light image and the surrounding part of the measurement object can be both imaged at an appropriate brightness.
According to the displacement sensor of the present invention, the controller under the observation mode may be adapted to repeatedly carry out one or a plurality of shots under the imaging condition where a measurement light radiated light image is not imaged at all or imaged substantially darker than an appropriate brightness, but a surrounding surface of the measurement object is imaged at an appropriate brightness and one or a plurality of shots under the imaging condition where with the measurement light source turned on a measurement light radiated light image is imaged at an appropriate brightness but a surrounding surface of the measurement object is imaged substantially darker than an appropriate brightness, in an alternating manner.
At this time, the controller may be adapted to display the obtained image every time on the image monitor. If an image substantially consisting solely of the surface image of the measurement object and an image substantially consisting solely of the measurement light radiated light source are shown in an alternating fashion in rapid succession, the viewer would get the impression that both of them are imaged at an appropriate brightness. If successive shots under a same imaging condition are performed in an alternating fashion, and the period for changing the imaging condition is long enough, the viewer can identify the images under different conditions as separate images and observe them in a proper positional relationship.
The controller may be adapted to display two images obtained under different imaging conditions one over the other on the image monitor. Even in such a case, it is still possible to display both the measurement light radiated light source and the surrounding surface image of the measurement object at an appropriate brightness level.
The controller may be adapted to repeatedly carry out one or a plurality of shots under the measurement mode and one or a plurality of shots under the observation mode, in an alternating manner. By so doing, the displacement measurement can be carried out while displaying the surface image of the measurement object on the image monitor. At this time, the controller may be adapted not to display an image obtained under the measurement mode on the image monitor but display an image obtained under the observation mode. By so doing, the displacement measurement can be carried out while verifying the state of the measurement position from the image captured under the observation mode. The controller may also be adapted to display one of an image obtained under the measurement mode or an image obtained under the observation mode in a selective manner. By so doing, the state of the image that is actually used for measurement can be verified whenever necessary.
The displacement sensor of the present invention may further comprise an illuminate for illuminating a measurement position on the measurement object and a surrounding region, the controller being adapted to turn on the illuminator under the observation mode.
The xe2x80x9cimaging condition under the observation modexe2x80x9d may include a brightness of the illuminator. According to this structure, even when brightness of the surrounding environment is not adequate, or the distance between the measurement object and sensor head is short, and the brightness of the surface of the measurement object is not adequate because the sensor head is located closely over the measurement object, a clear image can be displayed on the screen of the image monitor by illuminating the surface of the measurement object.
The light source for the illuminator may consist of a light emitting diode, an incandescent lamp, or any other small light source. Typical example of the light source for the illuminator can be found in a green light emitting diode. The illuminator preferably includes a light emitting optical system for radiating a small area having a prescribed shape (such as circular and square) including the measurement position.
In the displacement sensor of the present invention, the image acquiring optical system may comprise an oblique image acquiring optical system for capturing an image by viewing the measurement position of the measurement object and a surrounding region from an oblique angle, and a frontal image acquiring optical system for capturing an image by viewing the measurement position of the measurement object and the surrounding region from the front, and the two dimensional imaging device may comprise a two dimensional oblique image imaging device for photoelectrically converting an image obtained via the oblique image acquiring optical system and a two dimensional frontal image imaging device for photoelectrically converting an image obtained via the frontal image acquiring optical system, the controller under the measurement mode being adapted to compute a desired displacement according to a video signal from the two dimensional oblique image imaging device while the controller under the observation mode is adapted to display the measurement point of the measurement object and the surrounding region according a video signal from the two dimensional frontal image imaging device.
The xe2x80x9coblique image acquiring optical systemxe2x80x9d as used herein may comprise a lens array defining a light receiving light path, and may also comprise other optical elements such as mirrors and filters. xe2x80x9cViewing from an oblique anglexe2x80x9d means xe2x80x9cviewing from an oblique angle relative to a prescribed sensor mounting positionxe2x80x9d, and it literally means viewing obliquely from above when the measurement object is placed horizontally. More specifically, the incident angle of the light receiving optical system for measurement in the sensor head for a conventional displacement sensor should give an idea of what it is like (see c of FIG. 43 and g of FIG. 44).
The xe2x80x9cfrontal image acquiring optical systemxe2x80x9d as used herein may comprise a lens array defining a light receiving light path, and may also comprise other optical elements such as mirrors and filters. xe2x80x9cViewing from the frontxe2x80x9d means xe2x80x9cviewing from front relative to a prescribed sensor mounting positionxe2x80x9d, and it literally means viewing directly from above when the measurement object is placed horizontally. More specifically, the exit angle of the light emitting optical system in the sensor head for a conventional displacement sensor for irregular reflective surface objects should give an idea of what it is like (see f of FIG. 44).
According to this structure, under the measurement mode, a highly reliable measurement operation can be carried out relying only on the light image from the oblique image acquiring optical system while excluding the light image from the frontal image acquiring optical system. Under the observation mode, a peripheral image (the image of the measurement position of the measurement object and the surrounding region) free from distortion can be displayed on the screen of the image monitor relying only on the light image from the frontal image acquiring optical system while excluding the light image from the oblique image acquiring optical system.
The controller may be additionally adapted to operate under an image processing mode for computing a length or area on a surface of the measurement object by suitably adjusting a magnification factor of an image obtained by the frontal image acquiring optical system according to a displacement computed from an oblique image obtained by the oblique image acquiring optical system.
The image acquiring optical system may comprise an oblique image acquiring optical system for capturing an image by viewing the measurement position of the measurement object and a surrounding region from an oblique angle, and a frontal image acquiring optical system for capturing an image by viewing the measurement position of the measurement object and the surrounding region from the front, and the two dimensional imaging device may be used commonly for the two image acquiring optical systems.
In this case, the two dimensional imaging device may be placed at an intersection of light paths of the frontal image acquiring optical system and the oblique image acquiring optical system.
According to this structure, because a common imaging device can be used for the photoelectric conversion of the oblique image and the photoelectric conversion of the frontal image, it is possible to achieve the function to display an image of the surface of the measurement object on an image monitor without any distortion according to a video signal obtained from a sensor head without impairing the original function to measure displacements and at a low cost.
In this case, an exit light axis of the measurement light emitting optical system and an incident light axis of the oblique image acquiring optical system may be arranged symmetrically at a same inclination angle, and the two dimensional imaging device may be placed on an extension of an incident light axis of the frontal image acquiring optical system, the oblique image acquiring optical system comprising a light axis refracting mechanism for refracting an incident light axis onto the two dimensional imaging device.
According to this structure, because the sensor head can be applied to both regular reflective surface measurement objects and irregular reflective surface measurement objects, and the measurement light emitting optical system, oblique image acquiring optical system and frontal image acquiring optical system can be accommodated in the housing of the sensor head in a well-balanced compact manner.
The light axis refracting mechanism may be adapted in such a manner that light images formed on a light receiving surface of the two dimensional imaging device via the oblique image acquiring optical system and via the frontal image acquiring optical system move in a same direction on the light receiving surface of the two dimensional imaging device for a given change in the measurement displacement.
According to this structure, when the oblique image and the front image are shown on the screen of the image monitor one over the other, with a change in the displacement of the measurement object, the oblique image and the front image both move in a same direction, and this produces a natural impression to the user.
The displacement sensor of the present invention may further comprise shutter means for selectively shutting off one of a first light path reaching the two dimensional imaging device via the oblique image acquiring optical system and a second light path reaching the imaging device via the frontal image acquiring optical system either manually or electrically, so that the light path for the frontal image acquiring optical system is shut off under the measurement mode and the light path for the oblique image acquiring optical system is shut off under the observation mode.
According to this structure, one of the first light path reaching the imaging device via the oblique image acquiring optical system and the second light path reaching the imaging device via the frontal image acquiring optical system can be selectively enabled, and this prevents measurement errors during a displacement measurement by preventing the frontal image from reaching the imaging device and shutting off external disturbances, and allows the observation of the surface of the measurement object to be made without causing any distortion to the image by preventing the oblique image from reaching the imaging device during the observation of the object.
The mounting position of the shutter means may be found at the inlets of the light paths for the optical systems, intermediate points of the light paths or the terminal ends of the light paths. The shutter means may be of a mechanical type which shuts off the light path with a shutter plate or an electro-optical type using an electro-optical device (such as liquid crystal and PZT) which can be electrically controlled so as to be transparent or opaque, among other possibilities. xe2x80x9cSelective mannerxe2x80x9d can be achieved by any means as long as it can produce such a function as a result, and does not exclude the arrangement which can shut off or open both of the light paths at the same time.
The displacement sensor of the present invention may further comprise an illuminator for illuminating a measurement position of a measurement object and a surrounding region, a first optical filter having a band pass property for substantially permitting the passage of the measurement light provided in a first light path reaching the imaging device via the oblique image acquiring optical system, and a second optical filter having a band pass property for substantially permitting the passage of the illuminating light provided in a second light path reaching the imaging device via the frontal image acquiring optical system, the controller under the observation mode being adapted to turn on the illuminator.
According to this structure, by appropriately selecting the wavelengths of the measurement light and illuminating light, the selection of the light path can be accomplished automatically without using any special shutter means.
The measurement light source, illuminator light source, first optical filter and second optical filter may, for instance, consist of a red laser diode, a green light emitting diode, an optical band pass filter having a narrow pass band around the frequency component of the red laser as the first optical filter and an optical band pass filter having a narrow pass band around the frequency component of the green light emitting diode as the second optical filter, respectively.
In the displacement sensor of the present invention, the controller may be additionally adapted to operate under an image processing mode for computing a length or area on a surface of the measurement object by suitably adjusting a magnification factor of an image obtained by the frontal image acquiring optical system according to a displacement computed from an oblique image obtained by the oblique image acquiring optical system.
The sensor head according to the present invention may comprise a measurement light emitting optical system for emitting measurement light onto a measurement position of an measurement object from a prescribed angle, an oblique image acquiring optical system for capturing an image by viewing the measurement position of the measurement object and a surrounding region from an oblique angle, a frontal image acquiring optical system for capturing an image by viewing the measurement position of the measurement object and the surrounding region from the front; and a two dimensional imaging device for photoelectrically converting an oblique image obtained by the oblique image acquiring optical system and a frontal image obtained by the frontal image acquiring optical system into a video signal corresponding to the images.
The xe2x80x9cmeasurement light emitting optical systemxe2x80x9d as used herein may comprise a lens array defining a light emitting light path, and may also comprise other optical elements such as mirrors and filters. A light source for emitting light may be incorporated in the system or may be drawn from an external source via an optical fiber. An example of a light emitting light source consists of a red laser diode. The xe2x80x9cemitting anglexe2x80x9d may be either a regular reflective surface type described in connection with FIG. 43 or an irregular reflective surface type described in connection with FIG. 44.
The xe2x80x9coblique image acquiring optical systemxe2x80x9d as used herein may comprise a lens array defining a light receiving light path, and may also comprise other optical elements such as mirrors and filters. xe2x80x9cViewing from an oblique anglexe2x80x9d means xe2x80x9cviewing from an oblique angle relative to a prescribed sensor mounting positionxe2x80x9d, and it literally means viewing obliquely from above when the measurement object is placed horizontally. More specifically, the incident angle of the light receiving optical system for measurement in the sensor head for a conventional displacement sensor should give an idea of what it is like (see c of FIG. 43 and g of FIG. 44).
The xe2x80x9cfrontal image acquiring optical systemxe2x80x9d as used herein may comprise a lens array defining a light receiving light path, and may also comprise other optical elements such as mirrors and filters. xe2x80x9cViewing from the frontxe2x80x9d means xe2x80x9cviewing from front relative to a prescribed sensor mounting positionxe2x80x9d, and it literally means viewing directly from above when the measurement object is placed horizontally. More specifically, the exit angle of the light emitting optical system in the sensor head for a conventional displacement sensor for irregular reflective surface measurement objects should give an idea of what it is like (see f of FIG. 44).
According to this structure, because video signals corresponding to an oblique image of the surface of the measurement object and a frontal image of the surface of the measurement object can be obtained, it is possible to observe the surface of the measurement object by using the video signal corresponding to the frontal image while carrying out the displacement measurement using a video signal corresponding to the oblique image, and an image of the surface of the measurement object can be displayed on the image monitor without any distortion according to a video signal obtained from the sensor head without impairing the original function to measure displacements.
The two dimensional imaging device may be placed at an intersection of light paths for the frontal image acquiring optical system and the oblique image acquiring optical system.
According to this structure, because a common imaging device can be used for the photoelectric conversion of the oblique image and the photoelectric conversion of the frontal image, it is possible to achieve the function to display an image of the surface of the measurement object on an image monitor without any distortion according to a video signal obtained from a sensor head without impairing the original function to measure displacements and at a low cost.
In this case, an exit light axis of the measurement light emitting optical system and an incident light axis of the oblique image acquiring optical system may be arranged symmetrically at a same inclination angle, and the two dimensional imaging device may be placed on an extension of an incident light axis of the frontal image acquiring optical system, the oblique image acquiring optical system comprising a light axis refracting mechanism for refracting an incident light axis onto the two dimensional imaging device.
According to this structure, because the sensor head can be applied to both regular reflective surface objects and irregular reflective surface objects, and the measurement light emitting optical system, oblique image acquiring optical system and frontal image acquiring optical system can be accommodated in the housing of the sensor head in a well-balanced compact manner.
The light axis refracting mechanism may be adapted in such a manner that light images formed on a light receiving surface of the two dimensional imaging device via the oblique image acquiring optical system and via the frontal image acquiring optical system move in a same direction on the light receiving surface of the two dimensional imaging device for a given change in the measurement displacement.
According to this structure, when the oblique image and the frontal image are shown on the screen of the image monitor one over the other, with a change in the displacement of the measurement object, the oblique image and the front image both move in a same direction, and this produces a natural impression to the user.
The sensor head of the present invention may further comprise shutter means for selectively shutting off one of a first light path reaching the two dimensional imaging device via the oblique image acquiring optical system or a second light path reaching the imaging device via the frontal image acquiring optical system either manually or electrically.
According to this structure, one of the first light path reaching the imaging device via the oblique image acquiring optical system and the second light path reaching the imaging device via the frontal image acquiring optical system can be selectively enabled, and this prevents measurement errors during a displace measurement by preventing the frontal image from reaching the imaging device and shutting off external disturbances, and allows the observation of the surface of the measurement object to be made without causing any distortion to the image by preventing the oblique image from reaching the imaging device during the observation of the object.
The sensor head of the present invention may further comprise an illuminator for illuminating a measurement position of a measurement object and a surrounding region.
According to this structure, even when brightness of the surrounding environment is not adequate, or the distance between the measurement object and sensor head is short, and the brightness of the surface of the measurement object is not adequate because the sensor head is located closely over the measurement object, a clear image can be displayed on the screen of the image monitor by brightly illuminating the surface of the measurement object.
The sensor head of the present invention may further comprise a first optical filter having a band pass property for substantially permitting the passage of the measurement light provided in a first light path reaching the imaging device via the oblique image acquiring optical system, and a second optical filter having a band pass property for substantially permitting the passage of the illuminating light provided in a second light path reaching the imaging device via the frontal image acquiring optical system.
According to this structure, by appropriately selecting the wavelengths of the measurement light and illuminating light, the selection of the light path can be accomplished automatically without using any special shutter means.
The various structures of the present invention discussed above can be combined at will as long as technically possible.